Drawing ASTs for expressions: Correct Solution

For each of the Java expressions below:

• Draw an AST for the expression.
• Show how the expression evaluates at each node in the tree.

Be sure that your tree accurately reflects how Java would evaluate the expression.

Part 1

Given the following variables:

int prel = 4;
double bicol = 2.0;
double depep = 2.0;
double er = 5.0;

...draw the AST and evaluation results for the following expression:

prel / 9 - 2 + 2 / bicol - 7 * depep + er

Solution

Things to double-check in your solution:

• Do you have the left and right branches on the correct side?
• Did you indicate the difference between ints and floating point values?

Part 2

Given the following variables:

boolean mic = false;
boolean nas = false;
boolean pristasm = false;
boolean ca = false;
double ru = 2.0;
double houmed = 1.0;
double cuchial = 4.0;

...draw the AST and evaluation results for the following expression:

mic || (2 == 3 != !nas == pristasm && ca) != (7 == ru) || houmed >= cuchial

Solution

Things to double-check in your solution:

• Does your tree correctly reflect the precedence of && and ||?
• Did you correctly show short-circuiting? (That is when the right branch of && or || is never evaluated because the left branch already determines the answer.)

Part 3

Draw the AST and evaluation results for the following expression:

0 + 1 + (2 + "3" + 4 + 5 + "6" + 7 + 8)

Solution

Things to double-check in your solution:

• Did you indicate the distinction between ints and Strings?
• Are your left/right branches correct?

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